Mercenarys assault rifle dmg and effects (crit,poison,...) depend on the weapon you use, but which stat increases its dmg? agility since its ranged or is it depending on the weapon you use???
btw: assault rifle + unholy set is killer!
Pretty simple thou,
with warrior just put your points in strength and vitality
and upgrade whirl. in the beginning bloodlust might be helpful too.
try to get high damage swords and some +crit and leech items.
Now you can grind for ages without any trouble
Depends on weapon you use. (STR will increase damage if you use sword and AGI if bow)